1. Field of the Invention
The present invention relates to the production of metals in powder form by metallothermia, and, more especially, to the production of metals of Groups (IV)(B) or (V)(B) of the Periodic Table of Elements, or metals of the lanthanide series thereof, by lithiothermia.
This invention is particularly adopted for the production of a very pure titanium in powder form.
2. Description of the Prior Art
Techniques have long been known to this art for producing titanium, zirconium or the rare earths by reducing their chlorides with a powerful reducing agent, such as magnesium, sodium or calcium.
In the Kroll process, for example, titanium tetrachloride is chemically reduced by magnesium at about 1000.degree. C. according to the reaction scheme: EQU TiCl.sub.4 (g)+2 Mg (1).fwdarw.Ti (s)+MgCl.sub.2 (1)
The operation is carried out discontinuously in a steel reactor and in an inert atmosphere (helium or argon). The metallic titanium is then liberated in the form of sponge immersed in molten MgCl.sub.2. The sponge contains about 30% of its weight in impurities, particularly magnesium and magnesium chloride which are carried along when the sponge is precipitated. To obtain a very pure metal, the magnesium and chloride thereof must be distilled under a very high vacuum, a long and delicate operation which consumes great amounts of energy. The purified sponge is dried and then ground to obtain a titanium powder.
Another known process, similar to the Kroll process, but which uses sodium instead of magnesium at the stage where the TiCl.sub.4 is chemically reduced, has been styled the Hunter process. In this case, the titanium sponge forms at the center of the reactor and the solidified reaction medium is broken up by explosive agents, crushed, purified, and then dried in a stream of hot nitrogen.
U.S. Pat. No. 2,913,332 proposes the use of lithium as a reducing agent in the manufacture of titanium.
In this process, liquid titanium tetrachloride is poured onto a sheet of molten lithium floating on a bath of molten salts. The advantage of such a method over those described above is the fact that one can operate within much lower temperature ranges, on the order of 500.degree. C. This makes it possible to minimize pollution of the metal by the reactor materials, and also to use a simpler and thus less expensive technology.
Nonetheless, here again the titanium produced is in the form of sponge containing impurities, such as lithium and lithium chloride, which are transferred when the sponges are precipitated in the bath of molten salts.
In all cases, these processes thus have the marked disadvantage of producing metallic sponges which are difficult to purify. Other than the expensive and delicate purifying operations, particularly by distillation under vacuum, such processes also require an additional grinding stage to convert the desired metal into powder form.